This proposal seeks to determine the structure and regulation of synthesis of surfactant associated hydrophobic protein of 10,000 daltons, SAP-10p. This is a major protein component of mammalian surfactant. The proposal provides evidence that this is a unique lipid associated protein which is likely to play a role in metabolism and function of surfactant. It is likely that this protein is required for successful perinatal adaptation to air breathing and lack of surfactant is associated with hyaline membrane disease, a major factor in the increased morbidity and mortality of infants born prematurely. The protein will be isolated, amino acid composition and sequence determined from canine surfactant. Functional testing of its ability to alter the properties of phospholipids, their absorption and surface tension properties will also be tested. Synthesis and secretion of the protein will be determined in 35S-methionine labelled Type II epithelial cells in primary culture. Antisera and amino acid sequence will be generated for use in screening of a cDNA library generated from canine lung in a Lamdagt11 expression vector. Such cDNA's will be characterized by restriction mapping and sequenced. cDNA's for the canine 10,000 dalton protein will be isolated and used to screen a rat lung cDNA library for isolation and characterization of the rat cDNA for this protein. Developmental regulation of control of synthesis of the 10,000 dalton protein will be determined using the cDNA to quantitate mRNA levels in rat lung tissue in late gestation and by determination of synthesis and secretion of 35S-methionine labelled SAP-10p by organotypic cultures of fetal rat lung epithelial cells. These studies will clarify the origin, structure and function of the 10,000 dalton hydrophobic protein in surfactant and lead to further study of the molecular basis for the perinatal regulation of surfactant synthesis and secretion. This information will be valuable in the future therapy of hyaline membrane disease in newborn infants.